Update: Instructions verified through use as recently as 4/28/16
Gmail promises that you will never have to delete another email again. Yet the 7668 MB offered (as of today) in the free email accounts can easily fill-up over time if you send the occasionally large file. Sure you can search out attachments with the search operator “has:attachment” or “filename:zip”, but Gmail does not allow results to be ordered by attachment size and forces users to delete entire messages if they want to delete the attachments. You could purchase more storage from Google, starting at $5/year for 20GB, but then you’d be paying for your free email because you can’t delete large attachments – which defeats the purpose.
There are several blog posts recommending how to delete large attachments from gmail without deleting the email, none of which worked perfectly for me. My favorite is by Amit Agarwal. He recommends using the program IMAPSize, but when I tried it on my machine the software was not stable enough to handle the amount of email in my inbox and kept crashing, especially when I tried to sort by size. One upside of IMAPSize would have been the ability to delete lots of attachments at once. The method I list here can sort by attachment size, lets you delete them one at a time, and has never crashed on me.
Step 1: Download Mozilla Thunderbird and install. It’s open source, stable, and brought to you by the FireFox team (working as of v.45)
Step 2: Connect Thunderbird to your Gmail by setting up an “account” in Thunderbird. Thunderbird has all the Gmail settings preloaded.
Step 3: Go to the “All Mail” folder and then wait for your email to download. Thunderbird has to download all your email to your local machine. When this is done, which could be a few hours if you have tens of thousands of emails, you will be able to sort them.
Step 4: While inside the “All Mail” folder, right click the column so you can select the “attachment” column view. With the attachment view turned on, you can then sort the mail by attachment file size.
Step 5: Now that you can see the emails with the largest attachments, click on one and delete the attachment. To do this, click on the email and select the down arrow where it says “save”. The “delete” option will delete the attachment. Kind of.
Step 6: By Kind of, what I mean is that Thunderbird doesn’t really delete the attachment. What it does is that it creates an identical copy of the selected email without the attachment. To fully delete the attachment and reclaim your free Gmail storage space, the last step is to login to your Gmail, search for the email you selected in Thunderbird, and delete the original copy that has the full attachment. In this way you can delete the attachment and keep the original email.